This invention relates to engine control systems and, more especially, to aircraft engine control systems.
It is now becoming increasingly common for aircraft engines to be controlled by electrical signals rather than by mechanical and hydraulic means. The electrical control of engines enables greater flexibility, automation and efficiency of operation, together with a reduction in weight. Various arrangements are used to reduce the consequences of failure in the control system such as caused by damage to the components or to the programming software. For example, a limiter is commonly used, which may be either a mechanical or electrical device and which operates to prevent occurrence of an excessive engine condition, such as supply of too much or too little fuel for safe operation. The limiter acts to maintain operation just within the safety limits despite instructions from the control system to exceed those limits.
Two or more identical control lanes may be provided to the engine, each capable of operating independently, together with means for detecting malfunction of a lane and for switching to another lane. While such duplex arrangements can improve the ability of the system to operate safely, there can nevertheless be difficulties such as, in identifying which of the lanes is operating correctly. Such systems can also be too expensive for certain applications.